The present invention relates to endoluminal vascular prostheses, and, in one application, to self-expanding endoluminal vascular prostheses for use in the treatment of abdominal aortic aneurysms.
An abdominal aortic aneurysm is a sac caused by an abnormal dilation of the wall of the aorta, a major artery of the body, as it passes through the abdomen. The abdomen is that portion of the body which lies between the thorax and the pelvis. It contains a cavity, known as the abdominal cavity, separated by the diaphragm from the thoracic cavity and lined with a serous membrane, the peritoneum. The aorta is the main trunk, or artery, from which the systemic arterial system proceeds. It arises from the left ventricle of the heart, passes upward, bends over and passes down through the thorax and through the abdomen to about the level of the fourth lumbar vertebra, where it divides into the two common iliac arteries.
The aneurysm usually arises in the infrarenal portion of the diseased aorta, for example, below the kidneys. When left untreated, the aneurysm may eventually cause rupture of the sac with ensuing fatal hemorrhaging in a very short time. High mortality associated with the rupture led initially to transabdominal surgical repair of abdominal aortic aneurysms. Surgery involving the abdominal wall, however, is a major undertaking with associated high risks. There is considerable mortality and morbidity associated with this magnitude of surgical intervention, which in essence involves replacing the diseased and aneurysmal segment of blood vessel with a prosthetic device which typically is a synthetic tube, or graft, usually fabricated of Polyester, Urethane, DACRON(copyright), TEFLON(copyright), or other suitable material.
To perform the surgical procedure requires exposure of the aorta through an abdominal incision which can extend from the rib cage to the pubis. The aorta must be closed both above and below the aneurysm, so that the aneurysm can then be opened and the thrombus, or blood clot, and arteriosclerotic debris removed. Small arterial branches from the back wall of the aorta are tied off. The DACRON(copyright) tube, or graft, of approximately the same size of the normal aorta is sutured in place, thereby replacing the aneurysm. Blood flow is then reestablished through the graft. It is necessary to move the intestines in order to get to the back wall of the abdomen prior to clamping off the aorta.
If the surgery is performed prior to rupturing of the abdominal aortic aneurysm, the survival rate of treated patients is markedly higher than if the surgery is performed after the aneurysm ruptures, although the mortality rate is still quite high. If the surgery is performed prior to the aneurysm rupturing, the mortality rate is typically slightly less than 10%. Conventional surgery performed after the rupture of the aneurysm is significantly higher, one study reporting a mortality rate of 66.5%. Although abdominal aortic aneurysms can be detected from routine examinations, the patient does not experience any pain from the condition. Thus, if the patient is not receiving routine examinations, it is possible that the aneurysm will progress to the rupture stage, wherein the mortality rates are significantly higher.
Disadvantages associated with the conventional, prior art surgery, in addition to the high mortality rate include the extended recovery period associated with such surgery; difficulties in suturing the graft, or tube, to the aorta; the loss of the existing aorta wall and thrombosis to support and reinforce the graft; the unsuitability of the surgery for many patients having abdominal aortic aneurysms; and the problems associated with performing the surgery on an emergency basis after the aneurysm has ruptured. A patient can expect to spend from one to two weeks in the hospital after the surgery, a major portion of which is spent in the intensive care unit, and a convalescence period at home from two to three months, particularly if the patient has other illnesses such as heart, lung, liver, and/or kidney disease, in which case the hospital stay is also lengthened. Since the graft must be secured, or sutured, to the remaining portion of the aorta, it is many times difficult to perform the suturing step because the thrombosis present on the remaining portion of the aorta, and that remaining portion of the aorta wall may many times be friable, or easily crumbled.
Since many patients having abdominal aortic aneurysms have other chronic illnesses, such as heart, lung, liver, and/or kidney disease, coupled with the fact that many of these patients are older, the average age being approximately 67 years old, these patients are not ideal candidates for such major surgery.
More recently, a significantly less invasive clinical approach to aneurysm repair, known as endovascular grafting, has been developed. Parodi, et al. provide one of the first clinical descriptions of this therapy. Parodi, J. C., et al., xe2x80x9cTransfemoral Intraluminal Graft Implantation for Abdominal Aortic Aneurysms,xe2x80x9d 5 Annals of Vascular Surgery 491 (1991). Endovascular grafting involves the transluminal placement of a prosthetic arterial graft within the lumen of the artery.
In general, transluminally implantable prostheses adapted for use in the abdominal aorta comprise a tubular wire cage surrounded by a tubular PTFE or Dacron sleeve. Both balloon expandable and self expandable support structures have been proposed. Endovascular grafts adapted to treat both straight segment and bifurcation aneurysms have also been proposed.
Notwithstanding the foregoing, there remains a need for a structurally simple, easily deployable transluminally implantable endovascular prosthesis, with a support structure adaptable to span either a straight or bifurcated abdominal aortic aneurysm. Preferably, the tubular prosthesis can be self expanded at the site to treat the abdominal aortic aneurysm, and exhibits flexibility to accommodate nonlinear anatomies and normal anatomical movement.
There is provided in accordance with one aspect of the present invention, a moveable link for securing two portions of the wall of a tubular endovascular prosthesis. The link comprises a first wire portion having two side-by-side legs extending in a first direction and an apex thereon. A second wire portion is positioned adjacent the first wire portion. The first wire portion is wrapped around the second wire portion so that at least a portion of the apex faces in the first direction to at least partially entrap the second wire portion.
In accordance with another aspect of the present invention, there is provided an endoluminal prosthesis. The prosthesis comprises a tubular wire support having a proximal end, a distal end and a central lumen extending therethrough. The wire support comprises at least a first and a second axially adjacent tubular segments, joined by at least one folded link extending therebetween. The first and second segments and the link are preferably formed from a single length of wire.
Preferably, at least three folded links are provided between the first and second segments. The wire in each segment preferably comprises a series of proximal bends, a series of distal bends, creating a series of strut segments connecting the proximal bends and the distal bends to form a tubular segment wall. The folded link comprises a proximal or distal bend, together with a portion of two struts joined by the bend, extending through the loop formed by the other of the proximal and distal bends, to moveably link adjacent segments.
In accordance with a further aspect of the present invention, there is provided a method of making an endoluminal prosthesis. The method comprises the steps of providing a length of wire, and forming the wire into two or more zig-zag sections having proximal and distal apexes. The formed wire is rolled about an axis to produce two or more tubular elements positioned along the axis such that at least one proximal apex on one section axially overlaps with a distal apex on a second section. One of the proximal apex and distal apex is folded through the other of the proximal apex and the distal apex to produce a folded link. Preferably, the method further comprises the step of positioning a tubular polymeric sleeve concentrically on at least one of the tubular elements. In one embodiment, the tubular polymeric sleeve comprises PTFE.
In accordance with another aspect of the present invention, there is provided an endoluminal prosthesis. The prosthesis comprises an elongate flexible wire, formed into a plurality of axially adjacent tubular segments spaced along an axis, each tubular segment comprising a zig-zag section of the wire, having a plurality of proximal bends and distal bends. The wire continues between each adjacent tubular segment. At least two side-by-side wire segments joined by a first bend on a first tubular element extend through and interlock around a portion of a second tubular segment to provide a moveable link. The prosthesis is radially compressible into a first, reduced cross-section for implantation into a body lumen, and self expandable to a second, enlarged cross-sectional configuration at a treatment site in a body lumen.
Preferably, the prosthesis further comprises an outer tubular sleeve surrounding at least a portion of the prosthesis. Preferably, at least three segments are formed from the wire. The prosthesis has an expansion ratio of at least about 1:4, and an expanded diameter of at least about 20 mm to 30 mm in an unconstrained expansion.
Preferably, each axially adjacent pair of segments is characterized by an interface therebetween, wherein at least some of the proximal bends on one segment align with distal bends on the other segment to provide an opposing apex pair, and at least 30% of the apex pairs in a given interface are interlocked.
Further features and advantages of the present invention will become apparent to those of ordinary skill in the art in view of the disclosure herein, when considered together with the attached drawings and claims.